Very interesting method of wing construction. I will seriously consider this for a Zirolli B-25 that is awaiting time and building space.

couple of questions:
- on the inner cores that you used to 'pre-form' the sheeting, did you trim them down to allow for the thickness of the sheeting? Or is there enough flex in the inner core to allow for it?

- would you consider glassing the skins before forming them? Pros and Cons?

Sorry - have been off-line for a while - let me see if I can answer these Q's:

- on the inner cores that you used to 'pre-form' the sheeting, did you trim them down to allow for the thickness of the sheeting? Or is there enough flex in the inner core to allow for it?.

The core is cut to include the thickness of the sheeting - this means the bed is cut "WITHOUT" the sheeting thickness included in the foam. The middle core is therefore the same thickness as the finished wing. Hope that answers it well enough.

- would you consider glassing the skins before forming them? Pros and Cons?

You could but, depending on the wing, you will have a few to many joints you would need to take care of after the fact - LE is an example. This is something that I have considered for hollow molded witngs using foam beds as forms. I haven't tried this yet so do have too many comments to make about it.

She was primed, guide-coated, sanded, filled and re-sanded about a week or so ago. I haven't taken pictures of this as I think priming is priming!!! Suffice it to say however, I chose the PPG k-36 two part primer generally due to its fairly fast cure to sand time. The one thing I did do however, was only prime those areas that will be visible ONCE the aircraft is put together. No need, in my opinion, to add more weight than is necessary by painint those areas that will never be seen when the aircraft is assembled. I generally masked those areas that were not to be painted and went for it.

One other tip I gained from my automotive paint store was teh use of a guide coat. In my opinion, this is a great way to very easliy see the low spots and areas needing filler. The guide coat can be purchased in a rattle can for about 5 bucks a can. It is a laquer mist coat - i.e., it is a very thinned laquer and black in color. Let the primer cure well before misting the complete primed surface with the guide coat. Mist the guide coat on (just enough to mist-cover the primer, sand the primer and you will be left with very clear "black" areas that are low. Fill these and re-sand.

For those of you that have never used such an automotive primer, it is generally fairly simple to use. Mix it, reduce it if you need to, although generally not recommended by the manufacturer. Reducing is only really needed if you can't get the paint through the sprayer. I used a standard automotive spray gun at around 30 or so PSI. The very important item to note however, is that the primer is much thicker than paint and therefore you will need a larger paint nozzel than you would normally use for paint. Paint is typically sprayed throug a 1.4mm nozzel. PPG K-36 needs to be sprayed through a 2mm nozzel. Most automotive paint and spray gun suppliers will either have or can order a 2mm nozzel set for the guns they carry.

I found that it was only necessary to apply one coat of primer, guide coat and filler. Later, I will tell you why.

PPG K-36 dries to the touch in about 20 mins and can be gingerly handled to move stuff around. The pot life is about 45 mins at about 65 to 70 degrees so you should have plenty of time to spray parts or a pre-assembled aircraft.

For the filler, I started with a product recommended by my local automotive paint store - a product called Evercoat Easy Sand. This is essentially Bondo that has been modified for post-primer filling purposes. The problem with this stuff is that it has the cure time of bondo - i.e., minutes!!! It is very difficult to use this stuff on an aircraft and have it un-cured long enough for you to use. Soon after using some of the easy sand, I switched to the generic acrylic putty, in my case, again, by PPG and dark gray in color - much easier to work with.

So, a primed, sanded, filled and resanded P61 was ready for the next stage.

The next step was to paint the complete aircraft using the paint I was going to use for my finish coats - Klass Kote.

This layer of paint is essentially an "undercoat". I used Klass Kote white with a little black mixed in to make it a silimar color to the primer - gray. This was sprayed onto each component and allowed to cure overnight. The surface was then examined once more for any "dings" that I missed during the primer stage - surpisingly, there were very, very few!!!! The guide coat over the primer noted in the last post has some significant benefits in my opinion. I had about 10 to 12 minor areas that needed to be re-filled. Once these were filled, I spot sprayed the gray klass kote over these areas and again, allowed this to cure. Attached is a picture of the gray Klass kote sprayed booms. In my case, the gray Klass Kote is a very thin layer of paint - no real thickness to the coat. It's purpose, for me, was two fold:

1). Show up any dings I missed
2). Create a uniform, single color, HARD surface for the surface detailing

Primer is not a hard paint. I intend to use sharp scalpel blades to cut masking tape on the surface for many of the details I intend to add. As such, a really hard surface not prone to blade damage was important. The Klass Kote epoxy paint, when fully cured, is very hard and is an ideal surface for any blade related work (see later).

BTW, this is not a method I devised but a method described by Dave Platt in his Black Art series of tapes/DVD's.

Once I was totally happy with the surface finish, it was time to start marking panel lines - both "butt" type and "overlap" type and spraying more gray paint to highlight the details

As noted above, the third one is probably not best described as a panel and again, this is an idea taken from one of Dave Platts DVD's.

Starting with number 3 first, I have attached a couple of pictures but I am not sure they will show the process all that well. Fundamentally, the top and bottom of each rib on the elevator has, via appropriate masking, been built up with 3 to 4 layers of gray paint. Once this cured for about 3 days, the masking was pulled off and what remained was "raised" rib lines. I also did the trim tabs using the same method. After this was well cured, the whole surface will be vigorously rubbed with wire wool to round off the sharp edges where the masking was pulled away. The pictures do not show the final effect as the wire wool has not yet been used.

There are two pics, one with the masking and tape applied, the other after the masking has been removed. I'll cover methods 1 and 2 in a consequent post.

I used this method on the elevator and will also use it on the rudders and ailerons because of experience from others. In general, fabric covered, small surfaces like this do not apprently result in a fabric covered final look. This method has been noted as the best way to achieve a fabric covered effect for such a small item - we'll see!!!!

Images

Again, these are subtle features of the surface finish and do not show all that well in photos but the method is very similar to the rib "build-up" method described earlier.

On teh P61, overlap panels are predominantly where all the fairings are - around the fuse/wing joint and around the nacelle/wing joints. The two pictures below aain are not the best at showing this but fundamentally, the areas that were to remain at the same "deck" height as the rest of the fuse surface were masked. The area you see that looks a little different from the rest of the fuse around teh fairing was not masked. 3 to 4 layers of paint were then sprayed in this fairing area and left to cure. Once cured, the area was lightly sanded and the masking tape removed. What you are left with is a raised panel edge for an overlapping panel - pretty simple. Furter details like rivets will be added later.

Probably not much to say here as I suspect most of you know the drill.

Mark out the panel lines using the three-view, scaling etc etc.

I have attached a few pics of the panel lines I have marked on the surfaces including hatches, and in the case of the P61C, the dive brakes. These will be surface features as the dive brakes were non-operational for this version of the P61C.

The next step is to use Chartpak graphics tape (1/64" in my case) to trace the drawn panel lines. Once this is done, I will use the gray paint again to build up 3 to 4 layers in thin sprayed strips along each line. Once cured, pull the tape out, sand the surface and clean out any glue residue in the panel line from the tape with MEK. A very important note here is that the paint must be allowed to cure for about 4 to 6 days after you have sprayed the panel lines. MEK is a strong solvent and if the paint has not fully hardened, you will damage it.

Applying the Chartpac graphics tape will probably be something I do this weekend or next week. As I get the tape on and get ready for spraying, I will post again.

I am using HVLP guns. I have two. One is a standard gun with a 1 litre paint container attached to it - the make is a Warwick Industries Inc HVLP gun model 881H-14 (AC) used for automotive work. As purchased, it had a 1.4mm spray nozel which is what I used for the gray Klass Kote. Pressure for the Gray coat was about 35 to 40 psi at the gun - it's not highly critical. I have an air regulator directly at the gun hand grip and I adjust final pressure there. I also have a regulator at the wall outlet for my compressed air and that is set to 50psi - not that it really matters!!

This same gun was used for the primer except that I purchased a 2mm nozzel/needle/spray head separately for it. Again, similar pressure when spraying the primer.

The TWO things to remember are 1). test spray on a piece of wood or card BEFORE you spray the aircraft. Once you have your general flow and spray pattern nailed, go for it! 2). CLEAN, Clean, Clean!!! I used laquer thinner as the cleaner and you will need quite a bit of it - couple gallons for good cleaning. This is especially important for teh PPG type primer as this gels quite quickly (an hour or so). Clean the paint pot/gun after every use by spraying laquer thinner. At the end of the day, I then dismantle the gun and clean the parts separately in a pot of thinner with the generally supplied brush in the spray gun kit.

For the finer detail, like the panel lines etc, I am using a HVLP detail gun that I bought for about $50 from Harbour Freight. It is a Centrall Pneumatic Professional HVLP detail gun. There is no model number but it does have an item number - 46719. It has a 1mm nozel on it and sprays Klass Kote very well BUT ONLY AFTER A SMALL MODIFICATION!!!!!

The paint pot (5.3oz) does NOT have a breather hole in it. As such, after you spray for a few seconds, a vacuum is formed in the paint pot and the gun stops spraying!!! Not sure what the manufacturer was thinking! Easy to fix however, I drilled two 1/16" holes in the lid of the pot and problem solved! Pressure again is really something you adjust with the material you are spraying along with the fluid control. This gun is rated at 43psi max and I believe I sprayed at about 40psi with the 1:1:1 (paint:catalyst:reducer) mix of Klass kote.

Not much more to it. In general, any automotive HVLP gun will work as long as you remember for PPG type primer, you need a 2mm nozzel - typically not standard with a HVLP gun. Having both a 1.4 and 2mm nozzels REALLY completes the needs for primer and "undercoat". Given my experience with the undercoat, this same gun with teh 1.4 nozzel should be good for the color coats although I am leaning more toward the detail gun for this final layer.

My final suggestion, if you tend to be as impatient as I am, is you buy your guns from your local stores. They have parts, accessories etc ready at hand just in case something happens to the gun you have. Now I didn't do this with the detail gun but did for the other one. For me, it's just a little more convenient to run to the local store if I need parts rather than wait a week via mail order.

On reflection, I was not as clear in the area of pressure for a secific nozzel size so wanted to add this additional note. I too, asked a number of folks these same questions when I started spraying with HVLP's. The reality is that the pressure you use is somewhat related to the amount of paint you let out of the nozzel. The fluid control screw on the back of the gun controls this fiuld content.

What I have found that works the best is to set the pressure at around 35 psi and then adjust the rear fluid control screw to get the amount of paint you need when you press the trigger. The spray pattern is adjusted by the side air control knob. All the way in and the pattern is approximately round. As you unscrew the air control knob, more air is forced across the spray output and "flattens" the spray pattern to a fan shape. Rotate the front two ears on the spray gun and you change the direction of the spray fan. Certain jobs will be done right to left and need a vertical fan of paint. Certain jobs need to be done from top to bottom and need a horizontal fan spray pattern. Loosening the large ring around the spray pattern jets and rotating the air jets will allow you to have a spray fan at any angle in a 360 degree range to suit the pice being sprayed and the direction you need to spray it.

An example of a slightly different orientation than you would expect was when I sprayed the tail booms. I sprayed these while the whole boom was sat on the cowl mounts as you see in pictures above. My spray motion was top to bottom or vice versa. The spray pattern was horizontal.

So, bottom line, pick a psi of around 30 to 35 - for all paints. Adjust the fluid control nozzel for the right amount of paint output. Adjust your spray pettern with the air control knob, test spray. When you are happy, spray your part. This is te hway I do it - there is no formula that I know of.

For primer, if you need to build up teh primer, open the fluid control screw and spray more paint. Obviously, there is a point where too much comes out but it should be pretty easy to see that.

One more discussion point and I am trying to anticipate questions based upon the questions I had.

how much paint do I mix for teh gray coat????

This was one of my first questions - since I was going to use the gray coat method using KlassKote, how much paint should I mix up? Well, what I did was use a pint of Klasskote white, added the black I needed to make it gray and then reduce it 1:1. This gave me a quart. The Ziroli P61 is quite a lot of aircraft and I felt that a quart was more than enough to do the job. What you don't use, you can use on a different aircraft. To date, I have used just over a pint for the whole aircraft and anticipate using about another 1/3 pint for the panel lines.

Now, mixing for spraying - again, how much? Since I decided to spray the P61 in component form, my mixing was done in several small quantities. I had premixed the gray paint and reducer in a 1 quart pickling jar from my local KMART. I then used the prevail 6oz jars to mix each batch of paint. Prevail is the manufacturer of a small air based sprayer that my local auto paint store had. I bought 24 little jars in 2 x 12 packs specifically for mixing - not really expensive - about a buck each. The maximum amount I mixed for the largest component was 4 oz of paint/reducer (the 1:1 of the 1:1:1 mix). I then added the 2 oz of catalyst (satin catalyst BTW) to the 4 oz of paint/reducer. Shook it well and left for ten minutes in the jar, another shake, another ten minutes, another shake, another ten. After about 30 minutes, I poored this into the gun and sprayed.

If you are going to spray the whole aircraft, I would suggest bigger mixing jars and more paint. The Prevail jars already have 1 to 6 oz marks up the side of the jar so mixing to the correct ratios was easy AS LONG AS you don't pick up the jar after you have poured the paint in and before you have added the catalyst. Otherwise you will coat the inside of the jar with paint and you will have difficulty measuring the catalyst!

Sorry, on last point. Especially for the PPG primer, a NOISH spray mask is a must. That stuff is pretty toxic. I also sprayed the primer outside and used external air movement to clear the area of spray particles. You don't want to breath PPG or Dupont auto primer!!!!

For KlassKote on the other hand, I have been spraying that in my workshop without a mask - although probably not the wisest thing to do. From what I can tell, there is very little if any toxicity in the KlassKote paint. However, do not take this comment as a recommendation NOT to use a respirator. That stuff will hit your lungs if you don't and it is probably a safe bet to use a mask.

OK - next step? Chartpac tape on ALL the panel lines - chat to you in about a week!!!

OK, sometimes you just can't shut me up! I thought you might be interested in a source for Chartpak tape. I know for me that getting it locally is a little difficult.

Dave Platt recommends a 0.020" tape but this does not appear to be readily available - or at least I have not been able to find a source for it. The 1/64" (0.015") and 1/32" (0.031") in addition to larger sizes, are readily available from www.suppliesnet.com and fairly cheap. The 1/64" and 1/32" was $3.99 a roll compared to over $5 for locally bought 1/32".

I use the 1/64" stuff for panel lines and the 1/32" tape for simulated trim tabs if I do them this way.